This invention relates to the field of assisted walking for handicapped persons. It relates more particularly to walking assistance systems of the general type described by Petrofsky et al. in U.S. application Ser. No. 671,805, filed Nov. 15, 1984, and in a paper entitled "Feedback Control System for Walking in Man," Petrofsky et al., COMPUT. BIOL. MED. 14:135-149, 1984. Such systems utilize stimulation devices of the general type described in Petrofsky et al. U.S. Pat. No. 4,492,233 for stimulation of the legs of a handicapped person to produce a walking movement. They also utilize braces which may be of the type shown in Ser. No. 671,805 or of the reciprocating-gait type as described in a paper by Douglas et al. entitled "The LSU Reciprocation-Gait Orthosis," Orthopedics, July 1983, pp. 834-839. The present invention relates particularly to apparatus and method for controlling knee joint flexion in such walking assistance systems.
One of the problems with the above mentioned walking assistance systems is that smooth knee joint control has been difficult to obtain. The difficulty lies in the fact that no practical system exists for measuring the tension in the tendons when the knee is locked. Currently available sensors only measure the knee flexion angle. This has created an end looping problem when the computing system has attempted to achieve a fully extended knee attitude through use of a flexion angle sensor in closed loop control. Since negative flexion angles cannot be achieved, the flexion angle sensor never senses positive values thereof. The computer therefore must stimulate the flexion control muscles using control signals based upon single-sided sensor information. The control problem is particularly complicated since the stimulation control signal may require a maximum value for maintenance of a flexion angle of zero degrees.